A phrase used to describe something dealing with the body; usually sexual in nature.

However I have seen it used when discussing Genesis 2:21-25 in the Bible.

21 And the LORD God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; 22  And the rib, which the LORD God had taken from man, made he a woman, and brought her unto the man.

23  And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.

24  Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh. 25  And they were both naked, the man and his wife, and were not ashamed. (From the King James Bible)

Just a note about the above: Regardless of your religious tradition or political opinions (some feminists do not like a story where woman is created from man - even though they are later described as equal), the story at least in 24-25 is really a beautiful example of the equality of a sexual act.